A paste brazing material is used for integrally bonding members made of copper or a copper alloy by brazing. As described in JP-A-2000-197990, the paste brazing material is formed by mixing a high-molecular polymer and an organic solvent together with an alloy powder composed of phosphorus (P), nickel (Ni), tin (Sn) and copper (Cu). The paste brazing material is beforehand applied to an entire surface of a metal base material (i.e., copper alloy plate) to be bonded. Thereafter, the metal base material is heated for 5-10 minutes at temperature equal to or below 700° C. in vacuum or a reducing atmosphere furnace.
In this case, flux is not used, so that the melting point of the brazing material becomes low and cost of the brazing material is reduced.
However, the above-described brazing method is used only for a case where the brazing members have a simple flat plate shape. When an actual machine such as a heat exchanger is bonded by using the brazing method, an oxide film on the surface of a metal base material having a complex shape cannot be sufficiently removed by using the reducing gas and phosphorus (P) in the brazing material. Therefore, the brazing material cannot smoothly flow, and the bonding members of the actual machine cannot be sufficiently bonded.